Fluid indicators or "sight glasses" are often installed in the lines of refrigeration systems. Fluid indicators customarily incorporate a glass pane or other transparent aperture which allows a technician to view the refrigerant flowing in the line. By viewing the refrigerant as it passes through the indicator, a technician can determine that refrigerant is flowing satisfactorily and therefore the components upstream of the indicator are not plugged. By viewing the level and appearance of the refrigerant, the technician may also determine that the system needs to be charged with additional refrigerant or that the system needs to be charged with additional refrigerant or that the refrigerant is in need of replacement due to contamination.
Fluid indicators are typically installed by brazing the body of the indicator to the copper tubing through which the refrigerant flows. In conventional fluid indicators, the aperture portion is held in the body with low temperature solder material. As a result, the temperatues generated during brazing operations can cause the solder to melt. This destroys the liquid tight character of the fluid indicator and results in refrigerant leakage. To assure that the solder holding the aperture does not melt during brazing, it is conventional practice to apply a wet rag or chill block to the indicator body. These cooling devices maintain the solder in a solid condition while the tubing connections are brazed. The need to use these cooling devices is an inconvenience because they are time consuming and messy. In addition, even though the person installing the fluid indicator may use a cooling device, the solder seal around the aperature is sometimes destroyed.
Applicants' prior attempts to develop a liquid indicator with an aperture held in place by higher temperature brazing material instead of solder have been unsuccessful. The reason for this is that the indicator bodies are traditionally made of brass. Brazing material solidifies at such a high temperature that the brass body continues to contract after the brazing material has solidified. The contraction of the brass body after the brazing material is fixed, applies a compression force to the aperture. This resulted in the glass pane cracking either after the aperture was brazed in place or while brazing tubing to the fluid indicator.
Thus, there exists the need for a fluid indicator which may be successfully brazed to refrigerant tubing without the use of a chill block, wet rag or other cooling device.